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The aberrant behaviour observed in some Gammarids is correlated with the presence, in their brain, of mature metacercriae of Microphallus papillorobustus. Young cerebral larvae and mature thoracic or abdominal cysts of this Trematode do not induce alterations of behaviour in their hosts. Gammarus insensibilis and Gammarus aequicauda show different patterns in the distribution of M. papillorobustus larvae. Whereas many metacercariae are found in the thorax or abdomen of G. aequicauda adult, very few are present in this same location in G. insensibilis. Field data and experimental infections show that the post-cercariae encyst in the cerebroid ganglions in juveniles of both species as well as in adults of G. insensibilis; the post-cercariae encyst in the thorax or in the abdomen in adult G. aequicauda. The larvae could be attracted to the Amphipods' brain by a neurosecretion characteristic of young stages; this neurosecretion would still be produced at a high rate in adult G. insensibilis. |
